1. Field of the Invention
The present invention relates to a micro-actuator for fine movement of a magnetic head and to a method of producing the same.
2. Description of the Related Art
In recent years, reductions in size and thickness of magnetic disk devices, a kind of external storage device for computers, have been under way and, further, reduction in electric power consumption is requested. In addition, magnetic disk devices with higher recording density and larger capacity are demanded. Larger capacity of the magnetic disk devices can generally be realized by increasing the recording capacity per disk. However, an increase in recording density without changing the diameter of the disk leads to narrower track pitch; accordingly, the technical problem is how accurate the head device for reading and writing data on record tracks is positioned, and a head actuator with good positioning accuracy is desired.
Hitherto, in order to position a head with high accuracy in a magnetic disk device, generally, trials have been made to enhance rigidity of movable portions such as an actuator arm and raise the main resonance point frequency in in-plane directions. However, improvement of resonance point has a limit, and even if the in-plane resonance point of the movable portion can be raised, there is still the problem that vibration is generated due to spring characteristics of a bearing supporting the movable portion, resulting in a reduction of positioning accuracy.
As means for solving the above problem, a so-called two-stage actuator in which a second actuator for following the tracks, namely, a tracking actuator is mounted on the tip of an arm of a head actuator, has been proposed. The tracking actuator is for minutely moving the head provided at a tip portion of an arm, independently from motions of the head actuator, to achieve tracking of the head.
A two-stage actuator in which accurate positioning of the head is accomplished by utilizing laminate type piezoelectric elements as the tracking actuator for the two-stage actuator has been proposed. For example, two laminate type piezoelectric elements are disposed on both sides of an actuator arm, and a voltage is impressed in such a direction that the piezoelectric element on one side is elongated while the piezoelectric element on the other side shrinks, whereon the head is rotated in the direction of the piezoelectric element shrinking under the impressed voltage.
However, in the two-stage actuator utilizing the laminate type piezoelectric element according to the prior art, depolarization of the piezoelectric element occurs due to impression of a voltage in the direction reverse to the polarization direction of the piezoelectric element, exposing of the piezoelectric element to a high-temperature atmosphere, aging or the like; as a result, displacement per unit voltage gradually diminishes. Therefore, there is the problem that when the system is used for a certain long time, a desired stroke cannot be obtained. Furthermore, the two-stage actuator according to the prior art utilizing the laminate type piezoelectric elements has the disadvantage that productivity of the laminate type piezoelectric elements is bad, and high accuracy or precision of outer sizes of the elements is required, leading to high cost.
Two-stage actuators utilizing a shearing type piezoelectric element in place of the laminate type piezoelectric element having the above-mentioned many problems have been proposed in Japanese Patent Laid-open No. Hei 10-293979 and Japanese Patent Laid-open No. Hei 11-31368. A minute moving mechanism for head disclosed in the Japanese Patent Laid-open No. Hei 11-31368 has a three-layer structure in which two shearing type piezoelectric elements having different polarization directions are mounted on an electrode formed at the tip of a head arm, and a head suspension is mounted thereon through a movable member therebetween.
Therefore, this structure has a larger thickness from the head arm to the suspension, as compared with the conventional structure in which the suspension is fitted to the head arm with only a spacer. Thus, the two-stage actuator with the three-layer structure is unsuitable for reduction in thickness of the head actuator. Further, the increased thickness leads to greater distance between disk surfaces, whereby the number of disks mountable in the disk device is decreased, and storage capacity is also decreased as compared with the conventional disk device having the same height.
A minute moving mechanism for head which solves the above-mentioned problems has been proposed by the present applicant. In the invention of the previous application, an actuator base bent in a crank shape is fixed to a tip portion of an actuator arm. A base electrode, a shearing type piezoelectric element, a movable electrode and a movable plate are laminated and fixed on the actuator base, and a suspension is fixed to the movable plate. With the actuator base bent in a crank shape, the top surface of the actuator base and the top surface of the movable plate can be flush with each other, so that the minute moving mechanism for head utilizing the shearing type piezoelectric element can be made thinner.
In the invention of the previous application, electrical conduction must be provided between the shearing type piezoelectric element and the base electrode and the movable electrode, and, therefore, the base electrode and the movable electrode have been fixed to the piezoelectric element by use of a conductive adhesive. On the other hand, electrical insulation must be kept between the actuator base and the base electrode and between the movable electrode and the movable plate, and, therefore, fixation between the actuator base and the base electrode and between the movable electrode and the movable plate has been made by use of an ordinary insulating adhesive.
In the method of producing a micro-actuator using a conductive adhesive and an ordinary insulating adhesive according to the invention of the previous application, it is needed to selectively use the two types of adhesive, which leads to complicated production steps. Further, use of a conductive adhesive may easily be attended by generation of a short-circuit due to a mistake in production process. Thus, it is contemplated to contrive use of a single adhesive by using an insulating adhesive also for adhesion of the electrode and the piezoelectric element. However, where an adhesive is merely applied and cured, an adhesive layer thin enough to obtain electrical connection cannot be formed.
Therefore, a method of applying a pressure at the time of curing the adhesive is contemplated. However, where pressure is merely applied upon each lamination of component parts through an adhesive, the thickness of the adhesive layer on application of pressure is added to the thickness of component parts, so that variations of the thickness of the component parts will come out as large variations of the total thickness. Further, where electrical connection is envisioned, two shearing type piezoelectric elements are mounted on the base electrode, and the difference between the thicknesses of left and right piezoelectric elements may cause variations of the adhesive layer even if they are pressed in the same manner.
Accordingly, it is an object of the present invention to provide a method of producing a micro-actuator using a method of adhesion capable of securely providing electrical connection as required, irrespectively of variations of component parts.
It is another object of the present invention to provide a micro-actuator capable of selectively providing electrical connection and electrical insulation as required while using the same adhesive.
In accordance with an aspect of the present invention, there is provided a method of producing a micro-actuator, comprising the steps of: applying a first adhesive to a movable plate; placing a movable electrode on the first adhesive; clamping the movable plate and the movable electrode between a first stage and a first head, followed by heating for a first predetermined period of time while exerting a first predetermined press load onto the first head to semi-cure the first adhesive; applying a second adhesive to the movable electrode; placing a piezoelectric element on the second adhesive; clamping the movable plate, the movable electrode and the piezoelectric element between the first stage and a second head, followed by heating for a second predetermined period of time while exerting a second predetermined press load onto the second head to semi-cure the second adhesive; applying a third adhesive to an actuator base; placing a base electrode on the third adhesive; clamping the actuator base and the base electrode between a second stage and a third head, followed by heating for a third predetermined period of time while exerting a third predetermined press load onto the third head to semi-cure the third adhesive; applying a fourth adhesive to the base electrode; placing the piezoelectric element on the fourth adhesive; and clamping the actuator base, the base electrode, the piezoelectric element, the movable electrode and the movable plate between the second stage and a fourth head, followed by heating for a fourth predetermined period of time while exerting a fourth predetermined press load onto the fourth head to semi-cure the fourth adhesive.
Preferably, the first to fourth adhesives comprise a thermo-setting epoxy resin. Further preferably, the first to fourth adhesives are applied by use of a plurality of pins.
In accordance with another aspect of the present invention, there is provided a method of producing a micro-actuator, comprising the steps of: applying a first adhesive to a movable plate; placing a movable electrode on the first adhesive; clamping the movable plate and the movable electrode between a first stage and a first head, followed by heating for a first predetermined period of time while exerting a first predetermined press load onto the first head to semi-cure the first adhesive; applying a second adhesive to an actuator base; placing a base electrode on the second adhesive; clamping the actuator base and the base electrode between a second stage and a second head, followed by heating for a second predetermined period of time while exerting a second predetermined press load onto the second head to semi-cure the second adhesive; applying a third adhesive to the base electrode; placing a piezoelectric element on the third adhesive; clamping the actuator base, the base electrode and the piezoelectric element between the second stage and a third head, followed by heating for a third predetermined period of time while exerting a third predetermined press load onto the third head to semi-cure the third adhesive; applying a fourth adhesive to the piezoelectric element; placing the movable electrode on the fourth adhesive; and clamping the actuator base, the base electrode, the piezoelectric element, the movable electrode and the movable plate between the second stage and a fourth head, followed by heating for a fourth predetermined period of time while exerting a fourth predetermined press load onto the fourth head to semi-cure the fourth adhesive.
In accordance with a further aspect of the present invention, there is provided a micro-actuator comprising: an actuator base; a base electrode adhered to the actuator base by a first adhesive; first and second shearing-type piezoelectric elements having polarization directions opposite to each other and perpendicular to the element thickness direction, adhered to the base electrode by a second adhesive; a movable electrode adhered to the first and second piezoelectric element by a third adhesive; and a movable plate adhered to the movable electrode by a fourth adhesive, wherein the second and third adhesives are thin enough to allow electrical conduction respectively between the first and second piezoelectric elements and the base electrode and between the first and second piezoelectric elements and the movable electrode; and the first and fourth adhesives are thick enough to provide electrical insulation respectively between the actuator base and the base electrode and between the movable plate and the movable electrode.
Preferably, the first to fourth adhesives comprise a thermo-setting epoxy resin, and the second and third adhesives have a thickness of not more than 3 xcexcm.
In accordance with a still further aspect of the present invention, there is provided a method of producing a micro-actuator, comprising the steps of: applying a first adhesive to an actuator base; placing a base electrode on the first adhesive; clamping the actuator base and the base electrode between a first stage and a first head, followed by heating for a first predetermined period of time while exerting a first predetermined press load onto the first head to semi-cure the first adhesive; applying a second adhesive to the base electrode; placing a piezoelectric element on the second adhesive; clamping the actuator base, the base electrode and the piezoelectric element between the first stage and a second head, followed by heating for a second predetermined period of time while exerting a second predetermined press load onto the second head to semi-cure the second adhesive; applying a third adhesive to the piezoelectric element; placing a movable plate on the third adhesive; and clamping the actuator base, the base electrode, the piezoelectric element and the movable plate between a second stage having a first suction hole and a third head having a second suction hole, followed by heating for a third predetermined period of time while drawing under vacuum through the first and second suction holes and exerting a third predetermined press load onto the third head to semi-cure the third adhesive.
In accordance with a still further aspect of the present invention, there is provided a micro-actuator comprising: an actuator base; a base electrode adhered to the actuator base by a first adhesive; first and second shearing-type piezoelectric elements having polarization directions opposite to each other and perpendicular to the element thickness direction, adhered to the base electrode by a second adhesive; a movable plate adhered to the first and second piezoelectric elements by a third adhesive; a first wire for connecting the first and second piezoelectric elements; and a second wire for connecting either one of the first and second piezoelectric elements to the base electrode, wherein the base electrode comprises a first conductor pattern electrically connected to the first and second piezoelectric elements through the second adhesive, and a second conductor pattern electrically independent from the first conductor pattern and connected to the second wire, the second adhesive is thin enough to allow electrical conduction between the base electrode and the first and second piezoelectric elements, and the first and third adhesives are thick enough to provide electrical insulation respectively between the actuator base and the base electrode and between the movable plate and the first and second piezoelectric elements.
Preferably, the second adhesive comprises a thermosetting epoxy resin, and has a thickness of not more than 3 xcexcm.
In accordance with a still further aspect of the present invention, there is provided a method of adhering a plurality of members, comprising the steps of: applying a first adhesive to a first member; placing a second member on the first adhesive; clamping the first and second members between a first stage and a first head, followed by heating for a first predetermined period of time while exerting a first predetermined press load onto the first head to semi-cure the first adhesive; applying a second adhesive to the second member; placing a third member on the second adhesive; and clamping the first member, the second member and the third member between the first stage and a second head, followed by heating for a second predetermined period of time while exerting a second predetermined press load onto the second head to semi-cure the second adhesive.
The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing some preferred embodiments of the invention.